The increase in atmospheric pollution generated by exhaust emissions from conventional gasoline and diesel powered internal combustion engines have caused both federal and state governments to enact laws and establish regulations which impose even greater restrictions on the performance of motor vehicles in the areas of exhaust gas emission and fuel economy. As a result, over the past several years the automotive industry has increased its interest in using alternative fuels to meet the governmental emission requirements and fuel economy standards (CAFE), and to reduce dependence on foreign oil. Alternative fuels being investigated for potential use in automotive vehicles include compressed natural gas (CNG), liquid petroleum gas (LPG) and the like.
Alternative fuels typically have less energy per unit volume than gasoline or diesel fuel. However, they are generally advantageous since gaseous fuels are cleaner burning fuels. Gaseous fuels generate less noxious emissions than gasoline and diesel fuels and are able to better meet the increasingly rigorous governmental regulations.
Great strides have been made in developing control systems and components for gaseous fuel engines to meet the current government requirements. But, despite recent developments and the advantages of gas as a cleaner burning fuel, the exhaust emissions of a gaseous fuel engine still contain an undesirable amount of non-methane hydrocarbons, dust particle components and unburned hydrocarbons (methane). Moreover, the noxious emissions from gaseous fuel engines must be further reduced from current levels to meet future exhaust emission regulations.
In order to minimize the noxious emissions of gaseous fuel engines to meet future requirements, it is necessary to maintain an optimized air/fuel mixture for such engines at or near a selected point, such as the stoichiometric or a lean burn point. However, it has been difficult to accurately control the air/fuel mixture in a gaseous fuel engine because heretofore, the fuel injection systems have not been able to provide sufficiently accurate metering and control.
A typical gaseous fuel injection systems includes a pressurized fuel storage tank, a pressure regulator for reducing the fuel from a relatively high storage pressure to a lower working pressure (about one atmosphere), a fuel metering valve for controlling the gas supply to the engine, an air/gas mixer at the engine air intake and an engine management system for overall control and proper engine operation. Problems occur due to the fact that the injection of gaseous fuel into the intake manifold of the engine, where it is mixed with air, is sensitive to variations in manifold pressure, gas temperature and gas pressure caused by engine operating and environmental conditions. Such variations require extensive control techniques in order to maintain the desired quantity of injected fuel over the wide range of engine operating conditions. In addition, the fuel flow rate, which is much higher than in a conventional gasoline engine, requires a metering valve to control the flow rate over a large range, reducing its accuracy. Finally, the mixing of gaseous fuel and air produces problems simply due to the inherent difficulty of gas to gas mixing.
For accurate fuel metering, a combination of a digital and analog valve has been proposed. However, this type of valve is inherently complicated and difficult to control, and expensive to produce. Moreover, movement within the digital valve (or the duty cycle injector connected thereto) affects gas flow sensing accuracy. Installing a fuel valve at each cylinder injector aids in accurate fuel metering since the fuel flow rate is decreased due to the fact that several valves (one at each cylinder injector) are used instead of the one valve at the throttle. However, because the injector and intake valve are close together, there isn't sufficient time to mix the air and fuel thoroughly.
Accordingly, what is needed is an improved gaseous fuel injection system that will reduce noxious exhaust emissions and increase fuel consumption by accurately controlling the supply and ignition of the air/fuel mixture.
It is, therefore, a principal object of the present invention to provide a gaseous fuel injection system in which the air/fuel mixture can be accurately controlled to provide for increased fuel economy and reduced exhaust emission through a leaner burn operation.
It is another object of the present invention to provide a gaseous fuel injection system in which the air/fuel mixture can be accurately controlled to provide for maximum torque during various operating conditions of the engine.
It is a further object of the present invention to provide a gaseous fuel engine having increased fuel economy through a lighter weight, compact design fuel injection system.
It is still another object of the present invention to accomplish the above-stated objects by utilizing an apparatus which is simple in design and use, and economical to manufacture.
The foregoing objects and advantages of the invention are illustrative of those which can be achieved by the present invention and are not intended to be exhaustive or limiting of the possible advantages which can be realized. Thus, these and other objects and advantages of the invention will be apparent from the description herein or can be learned from practicing the invention, both as embodied herein or as modified in view of any variations which may be apparent to those skilled in the art. Accordingly, the present invention resides in the novel methods, arrangements, combinations and improvements herein shown and described.